Vasoactive intestinal polypeptide produces depolarization and facilitationof C-fibre evoked synaptic responses in superficial dorsal horn neurones (laminae I-IV) of the rat lumbar spinal cord in vitro

The actions of vasoactive intestinal polypeptide (VIP) were investigated on superficial dorsal horn (LI-IV) neurones in longitudinal slices of the rat lumbar spinal cord in vitro. Bath application of VIP (1-2 mM) cause depola rizations which were accompanied by a lowering of the threshold for excitat ion of the neu rone by current injection in the majority of cells studied. In some cases these depolarizations were very large and caused depolarizati on block and prolonged desensitization. An increase in spontaneous excitato ry postsynaptic potential (EPSP) frequency and amplitude was also produced by VIP. Synaptic responses evoked by peripheral nerve stimuli at intensitie s which recruited C-fibres were also facilitated by VIP. The principle acti on was on the later components of these responses which are dependent on C- fibre activation. EPSP summation evoked by trains of peripheral nerve stimu lation (wind-up) was also facilitated by VIP and the duration of these resp onses was clearly increased. These observations are discussed briefly in th e context of the possible role of VIP in neuropathic pain. (C) 1999 Elsevie r Science Ireland Ltd. All rights reserved.